The overall objective of this proposal is to continue the support at Vanderbilt University of an existing interdepartmental, multidisciplinary Population Research Center. The continuous support of the Center will maintain the efficiency of many population related projects now active at Vanderbilt and will permit development in new areas not presently represented. The research objectives of the Center include investigations on male reproductive physiology (sperm production, sperm biochemistry, sperm metabolism, sperm maturation, sperm capacitation, and development of male contraception), on female reproductive physiology (fertilization and implantation), and on reproductive endocrinology (mechanism of sex hormone action, pituitary hormones, and prostaglandins). Support is requested for an administrative core unit and eight core facilities (Hormone Assay, Histology & Photography, Electron Microscopy, Tissue Culture & Cytogenetics, Organic Chemistry, Cyclic Nucleotides, Lipid Analysis, and Prostaglandins). Support is requested for the development of two research programs one on the role of nucleoproteins in spermatogenesis and one on testis differentiation and spermatogenesis maintenance.